Process for working up cellulose derivatives



each case is determined by fwhieh is normally formed in the cellulose derivative on storing or on coming into contact with Patented Mar. 23, 1954 PROCESS FOR WORKING UP CELLULOSE DERIVATIVES Wilhelm Riihm,

Dormagen, Germany,

assignor to Farbenfabriken Bayer Aktiengesellschaft,

Leverkusen, many Germany, a corporation of Ger- No Drawing. Application September 11, 1950, Serial No. 184,333

Claims priority, application Switzerland September 14, 1949 5 Claims.

The present invention relates to improvements in the process for working up molten cellulose derivatives. The expression cellulose derivative herein comprises all meltable derivatives of cellulose, primarily organic esters and ethers of cellulose.

The invention relates to all kinds of processes in which the product passes through the molten state, for example, injection molding and spinning from the melt. In all these processes cellulose derivatives display the disadvantage of insufiicient stability. This instability may cause undesirable discoloration; it may also impair the mechanical properties of the finished products.

Therefore, such processing must be effected rapidly or at temperatures which are only slightly above the softening point. Needless to say, processing in this manner causes difficulties. Spinning of cellulose derivatives from the molten state, that is, without employment of any solvents, therefore, could not be effected on a large technical scale.

In accordance with the present invention it has been found that the melting point and thus the temperature at which the working up of the molten cellulose derivative may take place can be lowered considerably by imparting to the cellulose derivative a definite moisture content which is Within certain limits characteristic for each of the cellulose derivatives. The lower limit in the moisture content the open air. It should be mentioned that cellulose derivatives normally are produced in the anhydrous state and, when coming into contact with the atmosphere, they take up small amounts of moisture. Thus, the normally hydrolyzed cellulose acetate takes up about 1.5% of water, whereas the triacetate only takes up 0.1 to 0.3%. The moisture content required for the process of the present invention is definitely higher than that indicated above. On the other hand, the upper limit of the amount of water allowed is determined by the proportion of water that causes foaming of the molten cellulose derivative whose melting point is usually considerably above 100 C.

The present invention is based on the discovery that cellulose derivatives can take no substantial proportions of water without losing them at temperatures above 100 C. and that the such proportions of water considerably lower themelting points of the cellulose derivatives and therewith the temperatures required for the Working 2 up process. The moisture content to be used generally lies between about 05-10%. The preferred moisture content is at 8-9% with a hydro lyzed cellulose acetate derivative, and at about 6% with cellulose triacetate.

The content of water required in each case may be obtained in a simple manner by drying the cellulose derivative during its production only to the extent desired, or by spraying onto the derivative the amount of water still required above the content of moisture already present and then taking care that a uniform distribution occurs by mixing and storing in a sealed vessel. It is also possible to obtain the desired content of moisture by the action of steam on the cellulose derivative.

Preferably highly stable cellulose derivatives should be used for such working, up processes, for instance, cellulose derivatives obtained by means of perchloric acid or zinc chloride catalysts. Further stabilization can be eiiected by first removing the atmospheric oxygen with evacuation, or by replacing it by inert gases.

A further feature of the invention is that the cellulose derivatives are preferably in the finely divided state with a large surface, before being melted. Preferably loose or powdery precipitated cellulose derivatives are used. Their particle size should be such that they can be passed through a screen with a width of mesh of 1 mm. Although the derivatives then pass through the molten state, the particle size of the material to be worked up surprisingly influences the homogeneity of the finished product. This is true even when melting the cellulose derivatives in kneading machines, that is, to say under very high pressure.

Of course dyestuifs or pigments or other additive substances may be added to the cellulose derivatives during the preparatory stage of their production or in the melting vessel.

The following numerical data show the dependence of the melting point on the content of water. For carrying out the melting tests a. lever press with a specific pressure of 1.7 t/cm. was used. As starting materials there were used acetyl cellulose with a content of acetic acid of 52.5% (in the following marked I) on the one hand, acetyl cellulose with a content of acetic acid of 56.3% (in the following marked II), on the other hand, and a cellulose triacetate containing 60.8% of acetic acid (in the following marked III). The results obtained can be seen from the tables below, the water content being marked too high, if the formation of bubbles occurred in the lever press.

Content of Moisture, percent Acetyl Cellulose Melting point III No distinct M. P.

Content of Water too high. No distinct M. P.

160 C. Water content too high.

Content of Moisture, percent Melting point No distinct M. P. 160 C. 150 C.

water content too high.

If a cellulose tripropionate, precipitated in the usual manner and having a moisture content of is pressed at about 150 C. by means of a worm press through an orifice of 0.2 mm. diameter, the resultant monofil shows variations in diameter, although the mass in the worm was well kneaded during melting. These changes in diameter are caused by the non-homogeneous melting of the cellulose tripropionate. If, however, the same cellulose triproprionate is converted to a loose, powdery form prior to melting, for example, by milling until the particles pass through a screen with a Width of mesh of at most 1 mm., a perfectly uniform monofil is thus obtained which displays improved properties.

I claim:

1. In the process of shaping a composition consisting of a lower fatty acid ester of cellulose by melting it and then extruding it through an orifice, theimprovement which comprises incorporating sufiicient water in said cellulose ester,

before melting it, to bring its moisture content 5 substantially above the normal regain moisture but below saturation at the melting point of the cellulose ester.

2. A process as defined in claim 1 wherein a powdered cellulose ester is employed, whose particles will pass through a screen with a width of mesh of one millimeter.

3. A process as defined in claim 1 wherein a hydrolyzed cellulose acetate is employed, and its moisture content is brought to between about 8 and about 9 per cent.

4. A process as defined in claim 1 wherein cellulose triacetate is employed, and its moisture content is brought to about 6 per cent. 7

5. A process as defined in claim 1 wherein a finely divided cellulose propionate is employed, and its moisture is brought to between about 2 and about 5%.

WILHELM RCHM.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,516,225 Webb Nov. 18, 1924 1,987,610 Dreyfus Jan. 15, 1935 2,180,009 Malm Nov. 14, 1939 2,303,339 Dreyfus Dec. 1, 1942 2,303,340 Dreyfus Dec. 1, 1942 2,346,210 Farquhar Apr. 11, 1944 2,356,277 Schneider Aug. 22, 1944 2,571,975 Waltz Oct. 16, 1951 FOREIGN PATENTS V 40 Number Country Date 285,829 Great Britain Dec. 6, 1928 413,262 Great Britain Oct. '7, 1932 447,187 Great Britain May 6, 1936 OTHER REFERENCES Heuser: Cellulose Chemistry, 1943, page 44. 

1. IN THE PROCESS OF SHAPING A COMPOSITION CONSISTING OF A LOWER FATTY ACID ESTER OF CELLULOSE BY MELTING IT AND THEN EXTRUDING IT THROUGH AN ORIFICE, THE IMPROVEMENT WHICH COMPRISES INCORPORATING SUFFICIENT WATER IN SAID CELLULOSE ESTER, BEFORE MELTING IT, TO BRING ITS MOISTURE CONTENT SUBSTANTIALLY ABOVE THE NORMAL REGAIN MOISTURE BUT BELOW SATURATION AT THE MELTING POINT OF THE CELLULOSE ESTER. 